1. Field of the Invention
The present invention relates to an organic EL drive circuit and an organic EL display device using the same organic EL drive circuit and, in particular, to an organic EL drive circuit and an organic EL display device, which can reduce unevenness of luminance on a display screen of an organic EL panel of the organic EL display device used in a portable telephone set, etc., due to difference in characteristics between column driver IC's, can reduce manufacturing cost of the column driver IC's and, particularly, is suitable for high luminance color display.
2. Description of the Related Art
An organic EL display panel of an active or passive type organic EL display device for use in a portable telephone set including 396 (132×3) terminal pins (column pins) for column lines (anode side drive lines of organic EL elements or data lines) and 162 terminal pins for row lines has been proposed. These numbers of the terminal pins for column lines and row lines tends to be increasing.
With such increase of the number of terminal pins, a plurality of column driver IC's becomes necessary on, particularly, the column line side. For example, in a full color QVGA, the number of terminal pins for each of the three primary colors becomes 120, so that a total of 360 terminal pins are necessary, that is, three column driver IC's are presently necessary. Therefore, there is a problem that unevenness of luminance appears on a display screen of an organic EL display device, due to difference in characteristics between column driver IC's and, particularly, due to variation of drive currents of the column driver IC's.
For example, U.S. Pat. No. 6,747,417 (corresponding to JP2003-288045A) discloses a technique for solving the above problem, by restricting unevenness of drive currents between column driver IC's by utilizing the fact that values of integrated paired resistors are substantially equal.
Since, however, the constructions of the reference current generator circuits of the master column driver IC and the slave column driver IC of the U.S. Pat. No. 6,747,417 are different, these column driver IC's shall be manufactured separately, resulting in that the manufacturing cost of the driver IC's becomes high.
On the other hand, the size of organic EL display panel tends to be increased and a large size organic EL display panel requires three or more column driver IC's. Further, the increase of the number of terminal pins makes unevenness of drive currents of terminal pins considerable. Therefore, in order to improve unevenness of drive currents, highly precise drive currents are required. As to the drive current control utilizing the paired resistors, since unevenness of resistance values of the paired resistors influences the drive currents, the use of paired resistors can not respond to the present request of further reduction of luminance unevenness.